Static discharging paper



Nov. 6, 1962 H. R. DALTON 3,06

STATIC DISCHARGING PAPER Filed Feb. 11, 1960 W653, 7/ (PAPER FIBR 5) /.2 (WHITE co/vvuc T/VE P/GM E HAROLD RDALTON INVEN TOR.

BY X 4 6 ATTORNEY United States fatent 3,062,700 STATIC DISCHARGING PAPER Harold R. Dalton, Rydal Road, Jeukintown, Pa. Filed Feb. 11, 1960, Ser. No. 8,134 7 Claims. (Cl. 162138) This invention relates to paper manufacture, and more particularly it relates to the manufacture of paper which possesses inherent static discharging properties.

A principal object of the invention is to provide a paper which has a whitish or non-blackish hue, while at the same time possessing inherent electric conductivity sufficient to enable the paper to leak off static charges which tend to accumulate thereon.

One of the troublesome problems in the processing of large batches of paper, for example as continuous webs or sheets which are fed at relatively high speed through printing or similar equipment, is the tendency of the paper to accumulate electric charges by friction with cooperating parts of the machinery. Heretofore many solutions to the problem have been proposed, such as surface films such as aluminum; incorporation in the body of the paper complex organic compounds, carbon black, or metal powder; but only two approaches to the problem of discharging such static charge accumulations have met with any extended use. One requires elaborate electric contacting and grounding devices mounted on the various machinery parts to conduct the charge away from the paper surface. The other is to provide the paper with a coating of non-whitish conducting particles within the body of the paper which act as a discharge carrier. Examples of coatings are given in my prior Patent 2,887,632 and my Patent No. 2,940,941.

'It is clear that the coating method is not available where the paper is required to be free from surface coatings. While it has been proposed heretofore to impart electric conductivity to normally non-conductive paper by incorporating powdered carbon in the paper making batch, such method is not practical where the original whitish or non-blackish hue of the paper is to be preserved, since the carbon, even in small amounts, tends to give the paper a blackish or grayish appearance.

The present invention, therefore, has for one of its principal objects the manufacture of whitish or nonblackish paper which possesses inherent electric conductivity at least of sufiicient magnitude to enable the paper to be self-discharging for static charges that would otherwise tend to accumulate thereon.

A feature :of the invention relates to the manufacture of whitish or non-blackish paper which has incorporated therein during one of the paper manufacturing stages, for example during any of the well known pulp beating stages, a predetermined percent of a special whitish conductive pigment which has inherent electric conductivity sufficient for static discharging purposes.

Other features and advantages will be apparent after a consideration of the following detailed descriptions and the appended claims.

In the drawing,

FIG. 1 shows, in enlarged cross section, a portion of a paper prepared according to the invention;

FIG. 2 is a modification of the paper of FIG. 1.

As is well known, there are certain pigments or fillers which have been used quite generally to impart a whitish hue to papers and the like. Typical of such pigments are zinc sulfide, zinc oxide, barium sulfate, calcium carbonate, clay, satin white, and titanium dioxide. However, such fillers are electrical insulators and, therefore, are ineffective to impart electric conductivity to the paper in which they are embodied or on to which they are coated. I have disclosed in my prior Patent No. 2,887,632 a whitish Zinc oxide which is specially lQQ prepared so as to convert it from its normal character as a non-conductor so that it becomes, in itself, at least a semiconductor while preserving its whitish hue. Likewise, I have disclosed in my Patent No. 2,940,941, a titanium dioxide pigment which is also a conductor and preserves itswhitish hue.

I have found that by incorporating either or both of the said pigments in the paper pulp batch which is used in any conventional paper making machine, the finished paper preserves its whitish hue, opacity, surface properties, etc., and yet it possesses sufficient inherent electric conductivity so that it will, in contact with air, enable static charges to be dissipated. In other words, it is impossible for any appreciable static voltage to accumulate on the paper resulting from friction of the paper. with any adjacent surface.

As shown in the drawings, the finished paper 10 is free from carbon black or metallic fillers which have heretofore been considered necessary to prevent static accumulation. In accordance with the invention, the paper 10 has intimately mixed with the paper fibers 11 a predetermined percent of the said conductive white zinc oxide or the said conductive white titanium dioxide pigment powder, which pigment is indicated in the drawing by the numeral 12. The invention is not limited to any particular proportion between the paper fibers 11 and the conductive pigment 12, and the ratio of fiber to pigment by weight may vary from one percent to thirty percent, depending upon the whiteness, opacity, surface proper-ties, or conductivity, etc., desired in the finished paper.

Since methods of preparing paper pulp and its formation into paper sheets are well known in the paper making art, detailed description thereof is not necessary herein. Preferably, however, the said pigment, or combination of such pigments, is incorporated into the pulp batch during the so-called heater or refining stage, and the beaten pulp is then formed on any well known paper forming devices such as a Fourdrinier machine. Ordinarily the finished paper, therefore, will have the said conductive zinc oxide or titanium dioxide pigment distributed relatively uniformly through the thickness of the paper. However, if desired, the distribution of the said conductive pigment through the cross section of the paper may be graduated or graded to some extent, as indicated in the cross sectional view of FIG. 2, wherein the concentration of the pigment varies through the thickness of the paper. In the formation of paper on a Fourdrinier section of a paper machine, pigment or filler-s may be concentrated on the wire side of the sheet by controlling the 'freeness of the pulp, speed of the machine, or suction on the suction boxes.

It will be understood, of course, that the invention is not limited to the paper being of a whitish hue. For example, during the manufacture of the paper, any of the usual tinting materials may be mixed with the paper batch to imp-art a pastel or similar non-blackish color to the paper. In any event the paper, being substantially entirely free from carbon black or other powdered carbon, remains of a whitish or pastel hue and of the inherent desired static discharging conductivity.

Various changes and modifications may be made in the disclosed embodiments without departing from the spirit and scope of the invention.

What is claimed is:

1. An anti-static paper comprising compacted paper fibers intermixed with a white conductive oxide pigment powder chosen from the group consisting of conductive zinc oxide and conductive titanium dioxide, with the white conductive pigment powder constituting by Weight at least one percent of the finished paper.

2. A paper having semiconductor properties comprising a body of compacted paper fibers intermixed with a white conductive powdered oxide powder chosen from the group consisting of conductive zinc oxide and conductive titanium dioxide, with the white conductive pigment powder constituting by weight at least one percent of the finished paper.

3. A paper according to claim 2 in which the said powder is substantially uniformly dispersed through the cross sectional thickness of the paper.

4. A paper according to claim 2 in which the said powder is distributed in a substantially graded fashion through the cross sectional thickness of the paper.

5. A non-blackish paper having incorporated in the body thereof a combination of white conductive zinc oxide and conductive titanium dioxide pigment powders, with the powders constituting at least one percent of the finished paper by weight.

6. The method of making a paper which is inherently 4 conductive which includes the step of mixing with a paper pulp batch a white conductive oxide pigment powder chosen from the group consisting of conductive zinc oxide and conductive titanium dioxide, with the pigment powder constituting at least one percent of the finished paper by weight and forming a paper sheet from said pulp 7. The method according to claim 6 in which the said conductive oxide constitutes from one percent to thirty percent by weight of the paper-forming batch.

References Cited in the file of this patent UNITED STATES PATENTS 2,106,039 Satford Ian. 18, 1938 2,374,214 Kline Apr. 24, 1945 2,887,632 Dalton May 19, 1959 2,940,941 Dalton June 14, 1960 FOREIGN PATENTS 451,740 Great Britain Aug. 11, 1936 520,701 Great Britain May 1, 1940 

1. AN ANTI-STATIC PAPER COMPRISING COMPACTED PAPER FIBERS INTERMIXED WITH A WHITE CONDUCTIVE OXIDE PIGMENT POWDER CHOSEN FROM THE GROUP CONSISTING OF CONDUCTIVE ZINC OXIDE AND CONDUCTIVE TITANIUM DIOXIDE, WITH THE WHITE CONDUCTIVE PIGMENT POWDER CONSITUTING BY WEIGHT AT LEAST ONE PERCENT OF THE FINISHED PAPER. 